The field of the invention is web inspection systems and more specifically a system for encoding web (continuous) material with position information that can later be used to rapidly and precisely identify locations of interest on the web and performs some action based on those locations.
Hereinafter, while the present invention is applicable to various types of web materials and systems used to manufacture, process and repair such materials, unless indicated otherwise, the invention will be described in the context of paper manufacturing and systems used to locate and repair defects in large rolls of paper.
To meet the every increasing demand for paper products, the paper industry is constantly searching for ways to reduce costs and increase efficiencies of paper production. As in other industries, one way to reduce costs appreciably in the paper industry is to adopt mass production procedures. A paper manufacturing machine can rapidly produce extremely long (e.g., tens of miles) continuous ribbons of paper or webs. To store and handle these massive paper webs, a spindle (dowel) is mounted on a wind-up device, the leading end of the web is attached to the spindle and the spindle is wound at a high rate to take up slack in the web as the sheet emerges from an outlet end of the paper manufacturing machine. A paper web and associated spindle are referred to hereinafter as a reel.
After a complete reel (i.e., a full spindle) has been wound, the following end of the web is cut, the reel is removed from the wind-up device, a second spindle is mounted to the wind-up device and the process is repeated. Full reels are taken for further processing, by the paper manufacturer, or by end users (e.g., large printing companies, newspaper publishers, etc.). For this further processing, the reels are mounted on an unwind device that feeds a finishing machine, including paper coaters, patch and splice un-reelers, slitters, sheeters, folders, printing presses, etc.
Great effort has been exerted to minimize the number of manufacturing defects in paper webs like those described above. Nevertheless, a reel typically includes at least a small number of paper defects (e.g., 5-30 per roll) including holes, foreign objects, discolorations, edge tears, cracks, etc. At first blush, the small number of defects per reel may not seem troublesome, however, upon a more detailed perusal of paper processing and usage, it becomes apparent that even a small number of defects cannot be tolerated in many applications.
Perhaps the most important reason defects cannot be tolerated is that defects can cause finishing machines to malfunction. In this regard, as well known in the industry, even a small defect can, when subjected to the strains associated with high speed unwinding and other finishing activities, lead to an enlargement of the defect, the production of other defects, and even complete sheet breaks (a break in the web). When a sheet breaks, a large amount of sheet material is typically damaged as a large spinning unwind device typically takes a long time (e.g., minutes) to stop rotating and web material shoots off the reel during the slowing process. In addition, such breaks usually result in finishing machine downtime as the unwind device has to be stopped, scrap material has to be removed and discarded, the finishing machine line must be re-threaded and the finishing process has to be restarted.
One common method for dealing with paper defects is to identify and repair defects before they might impact further processing stages or compromise end-user quality standards. For example, an exemplary inspection system may include an inspection camera or cameras positioned between the output end of a paper manufacturing machine its wind-up device. The camera produces images of the complete area of paper manufactured and provides those images to an inspection processor. The inspection processor is programmed to identify defects in the received images. When a defect is identified, the inspection processor stores an indication of the defect type correlated with defect location along the web (hereinafter a “defect/location pairing”) in a database.
After a reel is full, the reel is removed from the wind-up device and mounted on the unwind device of another machine, a repair machine, with the free end (i.e., the following end) of the web linked to another wind-up device. The unwind and wind-up devices of the repair machine and the are controlled to unwind and rewind the paper web. The paper web can be stopped periodically to expose a defect or defect region for repair (e.g., a defect may be spliced out and a patch melded in its place). After a defect is repaired, the unwind and wind-up devices are again advanced until the next defect or region is exposed and can be repaired. After all defects are repaired, the remainder of the web is wound on the machine's wind-up spindle to form a complete reel and then the reel is removed and sent for further processing.
While inspection and repair systems like the one described above can yield reels free of critical defect, several difficulties have to be overcome in order to run such a system efficiently. In particular, to avoid a manufacturing bottleneck effect at a facility, the process of advancing between defects has to be rapid and stopping at defects must be precise. Overshooting or undershooting by a even a small amount can hide a defect and cause consternation as a system operator is forced to manually drive the system forward and backward to locate the defect. Advancing slowly between defects increases the time required for repair appreciably.
High speeds are not a problem as large motor systems are capable of rapidly accelerating even full reels to speeds of 8,000 feet per minute or more. Precisely stopping to expose a defect for repair, however, has proven to be more difficult. When a large paper reel is rotated at high speed, rotating momentum has to be overcome to stop the reel and the time required to stop the reel may be several minutes and may require several thousand reel rotations. Also, the paper must be accelerated and decelerated slowly (gently) to avoid ripping or deformation. Thus, the location of a defect has to be known well in advance of the defect being exposed in order to stop a rotating reel precisely for repair (e.g., so that the defect is exposed).
One solution for providing advanced warning that a defect is coming is to apply marks on the paper web that, upon unwinding, appear prior to the defect and that can be sensed to indicate that deceleration should commence. One particularly useful type of marking machine is positioned between a paper manufacturing machine's output and its wind-up device (e.g., proximate the inspection camera or cameras). The marking machine is linked to the inspection processor and provides “absolute position” mark sequences on the surface of a web and proximate a web edge as the web passes by. As the label implies, each absolute position mark sequence identifies a specific location along the length of the web. A typical mark sequence may include a series of marks that together form a code that can be readable at high speeds.
A processor at the repair machine, the repair processor, is programmed with an algorithm for de-coding the mark sequences to identify absolute web locations and is linked to access the defect/location pairings (i.e., the pairings stored by the inspection processor). The repair processor is also programmed with a stopping algorithm that can determine the typical slowing and stopping requirements of the machine, based on the current condition of the rotating reel (e.g. speed and acceleration). Specifically, the stopping algorithm attempts to predict the distance of web that would pass (be unwound) from the time a normal (non-emergency) slowing and stopping process commences until the web on the repair machine comes to a complete stop. For instance, the algorithm might calculate that slowing and stopping from a constant speed of 6,000 feet per minute should result in 7,000 feet of web being transported. In addition, the repair processor can commence processes to slow and stop the repair machine.
In addition to the components described above, the repair system also includes a camera or cameras linked to the repair processor and positioned between the unwind and wind-up devices of the repair machine to examine the mark sequences as the web is unwound for repair. The camera(s) provides images of the web near the edges to the repair processor which in turn identifies the mark sequences, decodes the sequences and thereby identifies location along the web length.
Having access to the defect/location pairings, being able to determine current web location and being programmed with the stopping algorithm, the repair processor should be able to precisely and efficiently stop the unwinding process to expose defects for repair. For example, assuming 7,000 feet are required to stop a high speed reel, the processor can be programmed to commence a stopping process when a mark 7,000 feet before a defect/location pairing is identified.
Unfortunately, while the system described above works well in theory, in reality there are several shortcomings. First, because of perceived hardware constraints, the industry has generally used relatively long marks to form mark sequences. For instance, an exemplary shortest possible mark in many cases is one or more yards long and may be ½ inch or more wide. While readily identifiable as a mark by many different types of camera systems, one or more yard long and relatively wide marks require excessive amounts of ink to produce and hence are costly. In addition, wide and long marks take up a relatively large amount of paper surface area and hence reduce the amount of paper useable by end users.
Second, marking hardware has some shortcomings that limit the characteristics of marks that can be uniquely distinguished with an acceptable degree of certainty. As known in the industry, mark making machines typically apply marks by spraying ink onto a surface of the paper web. While the beginning of a mark application is relatively precisely controllable (e.g., the turn on instant of a mark is controllable), the process of stopping mark application or turning off the mark sprayer is not very precise and, as a result, the ends of marks often “dribble” on past the points intended. This dribbling results in an unintended tailing effect. Hereinafter the unintended section of a mark will be referred to as a mark tail.
Because of the tailing effect, the differential between lengths of marks intended to indicate different information must be greater than the longest expected mark tail and the spaces between marks must also be greater than the longest expected mark tail. Thus, for instance, where an expected longest dribble or mark tail is 0.90 yards, the differential between marks intended to have different lengths that can be sensed has to be greater than 0.90 yards. Here, where a minimum mark length is 1 yard and numbers from 0 to 9 are to be represented by different length marks, the longest mark will have to be approximately 10 yards. Where value 9 is represented by a 10 yard mark, the value 999 may be encoded using a first ten yard mark (e.g., the first 9), a one yard space, a second ten yard mark (e.g., the second 9), a one yard space and a third ten yard mark (e.g., the third 9) so that the total length of the exemplary mark sequence associated with value 999 requires 32 yards.
Third, because of the length required to generate even a simple uniquely distinguishable mark sequence and the ink costs associated with such marks, most marking systems are limited to a small number of different mark sequences (e.g., 1000) and the space between marks equi-spaced along a multi-kilometer long web may be 1000 or more yards. Here, locations between mark sequences (i.e., intra-mark locations) have to be determined in some other fashion.
One way to identify intra-mark locations has been to provide an encoder on a roller proximate the repair machine unwind device that generates signals indicating roller velocity usable to determine web length travel from the most recent mark sequence. The web length travel is added to the location associated with the most recent mark sequence to determine instantaneous intra-mark location. Unfortunately, an encoder may not accurately measure the actual web movement, for a variety of reasons. For example, the web material may slip relative to the encoder's roll, the encoder may not be properly calibrated, and/or the material may shrink or stretch. Over a distance of 1000 yards or more, small errors may accumulate, resulting in a positional inaccuracy of several yards, yards causing the repair controller to stop the repair machine prior to or subsequent to desired defect exposure.
Fourth, when a reel of paper is first mounted on a repair machine, the material location is unknown until the first mark sequence is read. It is difficult to estimate the material location for numerous reasons: operators cut wraps of paper off the reel (e.g. to take samples for testing, to clean up the tail of the reel, or to prepare for threading), an unpredictable amount of material is transported during threading, etc. Thus, in cases where there is a great distance between mark sequences, it can potentially take a significant movement of web material before the first mark sequence is detected and decoded. This in turn can cause inaccuracies and failures when attempting to stop at a defect in the first portion of a reel that is being unwound.
Fifth, there are instances where a web breaks during the unwinding repair process and has to be repaired. Often to repair a web break, some paper material has to be discarded and hence the distance along a repaired web from the most recent location mark sequence is imprecise. To re-synchronize, the repair processor has to wait until the next location mark sequence is encountered and successfully read. In this case, the locations of defects prior to the next mark sequence (e.g., prior to re-synchronization), if any, cannot be precisely determined from the mark sequences and, in some cases, may not be repaired.
Sixth, despite efforts to apply clear and precise marks, sometimes marks are misapplied or misread. For instance, assume a sequencing system where a one yard mark corresponds to a zero, a two yard mark corresponds to a one and so on up to a ten yard mark corresponding to a 9. If the mark sprayer machine fails to apply ink (e.g., sputters) during a central section of a ten yard mark corresponding to a 9 value, the resulting two marks may be read as a 3 and a 4 (e.g., where the first mark is four yards long, the second mark is five yards long and the sputter accounts for a one yard space). Many other errors due to a sputtering mark sprayer machine are contemplated. Where errors of this type occur, in some cases, the repair processor may not be programmed to recognize the errors and incorrect control may result. In the alternative, some processors have been programmed to recognize mark sequences that are not supported by the system and to disregard the data related thereto. Where mark sequences are disregarded, the processor simply waits for the next mark sequence to relocate and, in the interim, may use encoder information to roughly determine location for control purposes. Here until a valid mark sequence is again read, imprecision is compounded.
Seventh, upon commencing reel advancement from one defect to another, prior known systems have tied commencement of the stopping process to velocity and distance (e.g., web length) to next defect. To this end, prior systems have recognized that, just as a reel spinning at a top speed or velocity requires a specific web length of unwinding to stop, intermediate speeds also require specific web lengths of unwinding to stop. For instance, if a reel spinning at a top speed of 6,000 ft./min. requires 7,000 feet of unwinding to stop, a reel spinning at 5,000 ft./min. may require 5,500 feet of unwinding to stop, reels spinning at 4,000 ft./min. may require 4,700 feet of unwinding to stop and so on. In some systems these velocity-required web length pairings are stored for use during unwinding. Here, upon commencing advancing movement toward a next defect, the top speed command signal is used to drive the reels and mark sequences and encoder data are used to identify current web length location and the web length to the next defect. In addition reel velocity is tracked and, when a web length paired with a stored reel velocity is equal to or less than the web length to next defect, the stopping process is started. For instance, consistent with the example above, where the reels are spinning at 4,000 ft./min and the web length to next defect is 4,700 feet the stopping process is commenced.
While systems like the one described above work well in theory, in reality such systems have important shortcomings. In particular, the assumption that there is a one to one pairing between reel velocities and web lengths required to stop is not completely accurate. Here, it should be sufficient to note that stopping length may depend on current acceleration as well as velocity. Thus, for instance, a reel rotating at a steady state 5,000 feet per minute may require less stopping length than a similar reel at 5,000 feet per minute that is accelerating at a high rate. Similarly, a full reel will typically require more stopping length than a half reel.
One way to deal with the shortcomings described above has been to adopt stopping algorithms that include some leeway for errors (i.e., a “fudge factor”) and that drives the reels at two different velocities. For instance, in the example above, where a high speed reel (e.g., 6,000 ft./min.) requires 7,000 feet of unwinding to stop, the stopping algorithm may be set to commence stopping at 7,500 feet. After a reduced velocity (e.g., at 500 ft./min.) is achieved (e.g., at 800 feet prior to the defect) the algorithm may maintain the reduced velocity until the defect is exposed.
Here, because of the location uncertainties described above, prior systems have required a relatively large fudge factor and hence a relatively long time to decelerate and stop proximate a defect. In addition, despite providing an encoder, these systems have been known to miss their target (i.e., the defect) by several yards thereby requiring a system operator to manually hunt for defects and thus further increasing the overall time required to find each defect.
While each individual process of locating and exposing a defect may not appear too burdensome, when a reel includes many (e.g., 30) defects, the cumulative additional time required to expose the defects is appreciable. Moreover, the enhanced stopping algorithms do not address the re-synchronization problems associated with web breaks described above.